Intermediate bulk containers are increasingly employed in cargo handling in transporting situations, especially for the carriage of particulate or pulverulent material. A typical IBC will be manufactured from a fabric woven from a polyolefin tape and have integral lifting loops. IBC's have to meet various national and international safety standards, for example it is normal to require a 5:1 safety ratio; that is, an IBC rated at one tonne should not break under loads of less than five tonnes. A particularly successful single trip IBC meeting these requirements is described in our UK Patent No. 1591091. In this, the side walls are made from a fabric having reinforced zones or areas of interwoven reinforcing yarn. The lifting loops are attached to such reinforced areas to produce an inexpensive light but sufficiently strong IBC.
One method of making such an IBC is to weave a fabric of four times the width of the eventual IBC having three pairs of reinforcing zones along its length and two further reinforcing zones approximately 15 cm inside each selvedge, making eight zones in total. The fabric is cut to length and the opposite selvedges sewn together. This produces the four side walls of an IBC having a pair of reinforced zones, or `tramlines`, adjacent each corner, one either side of the corner. A base is sewn in to the bottom edges of the side walls and the four lifting loops are attached one across each corner but each leg of a lifting loop being attached to a respective tramline. The lifting loops can be attached to the fabric before it is made up into an IBC except for the last lifting loop which crosses the side seam where the adjacent selvedges of the fabric are stitched together. This loop can only be attached when the selvedges are brought together, after which the side seam is completed. In this method of construction an average operator can produce about twelve to sixteen complete attachments (i.e. completed bags) per hour.